Figure REF (c) portrays a key difference in the encapsulation behaviour between the three cases, where the succesion of back pinch-off first and interior pinch-off second observed for clean interfaces is reversed in the presence of surfactants and the overall pinch-off dynamics are delayed (see the figure caption for the pinch-off times). This delay is accentuated for \(|\tilde{\tau }_{m}| > 0\) , as can be observed from the local peaks in \(\tilde{\kappa }\)  and \(\tilde{\tau }_{n}\)  of figure REF (b), which, in the case of \(|\tilde{\tau }_{m}| = 0\) , are already pulling the interface towards the channel centre, signalling the onset of capillary neck closure. Part of the role of Marangoni stresses can be seen in the green-shaded region of figure REF (a), where these tangential stresses counteract capillary forces at both the back and interior pinch-off regions. These observations are in complete agreement with the conclusions of [1]}, [2]}, [3]} for liquid threads, although we note that in our system the Marangoni forces exerted on the interface are not sufficient to escape pinch-off completely. The inversion of back and interior pinch-off times in contaminated interfaces can be attributed to the noticeably non-uniform surfactant distribution along the liquid cavity, which displays its highest values in the regions neighbouring the capillary neck at the back of the cavity, lowering surface tension and
providing additional disruption to neck closure in comparison to the interior cavity neck.
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